--- title: "T/F: tower height same for single/double circuit" subject: "Transmission and Distribution System Design" chapter: 4 key: "semester_8/transmission_and_distribution_system_design:tf-tower-height-single-double-circuit" source: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-tower-height-single-double-circuit site: BCT Engineering --- # T/F: tower height same for single/double circuit Transmission and Distribution System Design · Chapter 4: Conductor and Support Selection - Asked in: 2068 Bhadra (old course), 5 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/transmission_and_distribution_system_design/tf-tower-height-single-double-circuit - Whole chapter: https://www.bctengineer.com/md/semester_8/transmission_and_distribution_system_design/chapter-4 ## Question State whether the following statement is TRUE or FALSE and give reasons briefly: The height of tower is same for single circuit and double circuit for the same voltage level. ## Short answer FALSE. For the same voltage, a double-circuit tower is taller because it requires three cross-arm levels versus one or two for a single circuit, adding roughly one to two vertical spacing increments (e.g., about 4.9 m at 220 kV). ## Answer **FALSE.** For the same voltage, a double-circuit tower is generally **taller** than a single-circuit tower. - A **single circuit** has only 3 conductors. They can be placed horizontally (one cross-arm level) or in a triangle (two levels). The tower height is roughly ground clearance + maximum sag + one level of spacing + earth wire height. - A **double circuit** has 6 conductors. They are normally arranged as two vertical circuits on either side of the tower, giving **three cross-arm levels**. The height becomes ground clearance + sag + $2Y$ + earth wire height, where $Y = l + a$ is the vertical separation (about 4.9 m at 220 kV). | Item (220 kV, same span) | Single circuit | Double circuit | |---|---|---| | Conductor levels | 1–2 | 3 | | Typical tower height | ≈ 30–35 m | ≈ 40–45 m | | Base width / weight | Smaller | Larger (about 1.5–1.8 times) | The ground clearance and sag are the same for both, but the extra cross-arm levels add about one to two times $Y$ to the double-circuit tower. Double-circuit towers also carry twice the conductor loads, so their base and weight are larger too. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. The tower height is the same for single and double circuit at the same voltage. Is this true? A. True, the voltage fixes the height B. False, a double-circuit tower is generally taller C. False, a single-circuit tower is always taller D. True, only the base width differs Answer: B. A double circuit has 6 conductors on three cross-arm levels, so its tower is taller. (Key point: True or false verdict) 2. Why is the double-circuit tower taller? A. It has more cross-arm levels, adding about 1 to 2 times Y B. It needs a larger ground clearance C. Its sag is larger D. It uses a longer earth wire only Answer: A. Ground clearance and sag are the same, but extra cross-arm levels add vertical spacing Y = l + a. (Key point: Reason for extra height) 3. Besides height, what else is larger for a double-circuit tower? A. Nothing, it is identical B. The conductor sag C. The ground clearance D. Base width and weight, as it carries twice the conductor loads Answer: D. Twice the conductor loads gives a larger base and heavier tower. 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